The present invention relate broadly to coincidence detectors, and in particular to a three-stage binary coincidence detector apparatus with adaptive constant false alarm rate (CFAR).
In the prior art it is well known that a radar apparatus often is operated in an environment in which the limitation of its services results not only from the internal noise, but also from undesired echoes, such as for example, land or sea returns, the disturbing effect of rain clutter, etc. In order to distinguish the return which results from a target rather than from noise, it is possible to have recourse to a constant threshold, but the presence of undesired echoes, which may mask the useful signals, makes such a technique for discrimination unacceptable.
These drawbacks result substantially from the nonconstancy of the probability of false alarm, can be seen in the radar systems using computers to handle the data relating to the target, as well as in those in which the decision regarding the presence or the absence of a useful echo, is given by an operator who decides on the basis of the visual representation. It is therefore of the greatest importance to overcome this drawback, to maintain constant the probability of false alarm.
In the prior art, spatially-varying clutter statistics and dense target environments impose difficult requirements on a conventional adaptive detector. The result is that the detector fails to maintain a constant false alarm rate as clutter statistics vary and also fails to accommodate target-to-target interference as target enters the CFAR block. There is a further problem for the conventional adaptive detector which fails to accommodate the target-to-target interference as targets pass through the clutter cells in the detector. The clutter cells are usually referred to as a CFAR block which forms the clutter avergage. When the target enters the CFAR block, the target signal will raise the clutter average and degrade the ability to detect the nearby target incidently located in the detection cell. The detection degradation due to the target interference has been found to be unacceptable especially if radar operates in very heavy target environments. To eliminate the above-mentioned problems for target detection, a unique three-stage binary coincidence detector apparatus is presented.